Seems a bit late...

Our swallows were late nesting this year. The male seemingly having difficulties in attracting a female to help him build a nest in our shed whose door I had hacked a chunk out of the top, to let swallows in and keep Magpies out. Eventually they sussed it and raised a broodof six  which fledged in late July. They managed a second brood of five that fledged a couple of weeks ago. I though last weekend they had gone but last night noticed swallows hawking around the yard as it grew dark and then entering the shed to roost. And then same thing again tonight. Presumably they are our birds but where have they been during the day? Why have they not gone and when will they go?  Answers on a signed blank cheque please!